Devices for holding intermediate positions and articles that contain the same

ABSTRACT

Disclosed herein is a strut assembly  10  comprising a locking device  11  in operative communication with a piston  3 , wherein the locking device  11  comprises an active material operative to resist motion of the piston  3  in response to an activation signal. Disclosed herein too is a method of operating a strut assembly  10  comprising displacing a suspended body  60  in mechanical communication with a piston  3 ; activating an active material in operative communication with the piston  3 ; and controlling the motion of the suspended body  60.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/552,791 filed Mar. 12, 2004, and is a divisional of U.S.non-provisional application Ser. No. 11/078,847, filed on Mar. 11, 2005,the entire contents of which are hereby incorporated by reference.

BACKGROUND

This disclosure relates to devices for holding intermediate positionsand articles that contain the same.

Strut assemblies are often used in automobiles to facilitate theopening, locking and positioning of doors, trunks, hoods, tail-gates, orthe like. They are also used in residential homes to facilitate thelocking of doors, storm doors and windows. These assemblies generallyrequire manual effort to initiate locking when it is desired topartially or fully open an article (e.g., door, window, or the like)that is in operative communication with the strut assembly. For example,a door that is in operative communication with a strut assemblygenerally has a small washer that is manually adjusted to facilitatelocking of the strut assembly in order to prop open the door. This canpose a problem for users of articles to which the strut assembly isattached, when for example, the user has both arms engaged in otheractivity such as carrying cargo, or the like.

In addition, strut assemblies that require manual interaction tofacilitate locking are generally not easily accessible. For example,strut assemblies that are used for propping open storm doors aregenerally located at the top of the storm door and are often not easilyaccessible to shorter people. Many practical benefits can accrue fromthe ability to hold the swing panel open in any given position until itis moved to a new position e.g. an opened tailgate will remaincomfortably within the reach of shorter users, the trunk swing panelwill not beat against a piece of luggage that extends outside the trunk,etc.

It is therefore desirable to use strut assemblies that offeropportunities for automated locking. It is also desirable to use strutassemblies that can be used to lock an article that is in communicationwith the strut assembly in one position until it is desired to displacethe article to a new position in which it can be locked once again.

SUMMARY

Disclosed herein is a strut assembly comprising a locking device inoperative communication with a piston, wherein the locking devicecomprises an active material operative to resist motion of the piston inresponse to an activation signal.

Disclosed herein is a strut assembly comprising a piston in slideablecommunication with a housing; a locking device in operativecommunication with the piston, wherein the locking device comprises atilt washer in operative communication with an active material, whereinthe tilt washer is operative to resist the motion of the piston.

Disclosed herein is a strut assembly comprising a piston in slideablecommunication with a housing; a locking device in operativecommunication with the piston, wherein the locking device comprises asleeve; and an active material in operative communication with thesleeve; wherein the sleeve is operative to control the motion of thepiston.

Disclosed herein is a strut assembly comprising a piston comprising apiston head and a piston rod; wherein the piston is in slideablecommunication with a housing; a locking device in operativecommunication with the piston, wherein the locking device comprises aplate in operative communication with a piston head; wherein the plateis in slideable communication with the piston rod; a spring stackdisposed between the plate and the piston head; and an active materialin operative communication with the plate; wherein the active materialupon activation is operative to control the motion of the piston.

Disclosed herein too is a strut assembly comprising a piston comprisinga piston head and a piston rod; wherein the piston rod is in slideablecommunication with a housing; a locking device in operativecommunication with the piston, wherein the locking device comprises oneor more protrusions fixedly attached to a piston head; a wave-liketubular guide comprising an active material, wherein the wave-liketubular guide is in slideable communication with the protrusions; andwherein the wave-like tubular guide is operative to control the motionof the piston.

Disclosed herein too is a strut assembly comprising a piston comprisinga piston head and a piston rod in slideable communication with ahousing; wherein the piston head comprises a portion having one or moreelastic members; one or more brake shoes, wherein the brake shoes are inoperative communication with the elastic members; and an active materialin operative communication with the brake shoes; wherein the activematerial is operative to control the motion of the piston.

Disclosed herein too is a strut assembly comprising a piston thatcomprises a piston head and a piston rod, wherein the piston is inslideable communication with a housing; wherein the housing comprises anelectrorheological fluid or a magnetorheological fluid and wherein thepiston head comprises an optional permanent magnet, and anelectromagnet; and wherein the optional permanent magnet and theelectromagnet are operative to control the motion of the piston.

Disclosed herein too is a locking device comprising a pivot pin havingdisposed thereon a ball disk comprising balls; a long arm and a shortarm in rotary communication with a pivot pin; wherein the short armcomprises detents disposed upon a surface that is opposed to a surfacein contact with a surface of the long arm; and a cylindrical housing incommunication with a surface of the long arm in opposition to a surfacein contact with the short arm, wherein the housing comprises anactuator, a piston and a spring, and wherein the actuator comprises ashape memory material operative to disengage the balls from the detents.

Disclosed herein too is a method of operating a strut assemblycomprising displacing a suspended body in mechanical communication witha piston; activating an active material in operative communication withthe piston; and controlling the motion of the suspended body.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 is an exemplary schematic depiction of a strut assembly 10 thatcomprises a locking device 11. The locking device 11 comprises a tiltwasher 22 in operative communication with an active element 20 thatcomprises an active material;

FIG. 2 is an exemplary schematic representation of a side view and afront view of a section of the strut assembly 10 depicted in the FIG. 1;

FIG. 3 is an exemplary schematic representation of the mode of operationof the locking device 11 of the FIG. 1;

FIG. 4 is an exemplary schematic representation of one possible locationof the locking device 11 that comprises a sleeve 32 in operativecommunication with an active element 20. The locking device can bedisposed in the housing if desired;

FIG. 5 is an exemplary schematic depiction of the strut assembly 10wherein the locking device 11 is in operative communication with apiston rod 12. The active element 20 and the return spring 30 permitcontrol of the motion of the piston rod 12;

FIG. 6 is another exemplary schematic depiction of the strut assembly 10wherein the locking device 11 is in operative communication with apiston rod 12. The active element 20 and the return spring 30 permitcontrol of the motion of the piston rod 12;

FIG. 7 is an exemplary schematic depiction of the strut assembly 10wherein the locking device 11 is in operative communication with apiston rod 12. The piston rod 12, the active element 20 and the sleeve32 are concentrically arranged with the active element 20circumferentially disposed upon the sleeve 32;

FIG. 8 is an exemplary schematic depiction of the strut assembly 10wherein the locking device 11 is in operative communication with apiston rod 12. The locking device comprises a spring stack 26, whichwhen compressed controls the motion of the piston rod 12;

FIG. 9 is an exemplary schematic depiction of the strut assembly 10wherein the locking device 11 comprises a wave-like guide 36 inoperative communication with a piston 3. The piston 3 comprises one ormore protrusions 48 that are in slideable communication with the guide36 that comprises a wave-like inner surface;

FIG. 10 is an exemplary depiction of the construction of the wave-liketubular guide 36;

FIG. 11 is an exemplary depiction of a strut assembly 10 that comprisesa locking device 11 wherein the piston head comprises brake shoes 54that are in operative communication with the piston rod 12 and inslideable communication with the housing 2;

FIG. 12 is an exemplary depiction of a cross-sectional view of thecentral portion 52 of the piston head 12 displayed in the FIG. 11;

FIG. 13 is an exemplary depiction of a strut assembly 10 that comprisesa locking device 11 wherein the piston head 14 comprises brake shoes 54that are in operative communication with the piston rod 12 and inslideable communication with the housing 2. The central portion 52 ofthe piston head 14 comprises a groove that engages with the lockingrings 62 to lock the strut assembly 10;

FIG. 14 is an exemplary depiction of a cross-sectional view of thecentral portion 52 of the piston head 12 displayed in the FIG. 11;

FIG. 15 is an exemplary depiction of a strut assembly 10 wherein thehousing 2 comprises a magnetorheological fluid. The displacement of thestrut assembly can be controlled by using a magnetic field disposedwithin the housing to change the viscosity of the magnetorheologicalfluid;

FIG. 16 is a depiction of an exemplary embodiment of a front view of apivot detent locking device 11;

FIG. 17 is a depiction of an exemplary embodiment of a rear view of apivot detent locking device 11;

FIG. 18 depicts a sectional view of one embodiment of the pivot detentlocking device 11 when in the locked position; and

FIG. 19 depicts a sectional view of one embodiment of the detent-lockingdevice 11 in its unlocked position.

DETAILED DESCRIPTION

Disclosed herein are locking devices employed in conjunction with strutassemblies that can advantageously be used to lock an article (asuspended body) in a desired position. The locking device advantageouslycomprises an active element that is in a frictional relationship with amoveable component of the strut assembly, such as for example, thepiston, thereby facilitating a locking of the suspended body. Africtional relationship is one wherein resistance is applied eitherdirectly or indirectly to the motion of a moveable component of thestrut assembly due to friction between the moving components. In oneembodiment, the locking device is in operative communication with apiston, wherein the locking device comprises an active materialoperative to resist motion of the piston in response to an activationsignal. In another embodiment, the locking device is in operativecommunication with the housing and is adapted to resist the motion ofthe housing. The locking device can be disposed on the cylinder and canbe in operative communication with the piston or can be disposed on thepiston and can be in operative communication with the cylinder. Thelocking device can be used to control the motion of the suspended bodyand can lock the suspended body when desired.

The strut assembly is disposed between the suspended body and asupporting body and is in operative communication with the suspendedbody and the supporting body. The locking devices can be deployed eitherinside or outside the strut assemblies. The locking devicesadvantageously employ active materials, i.e., materials that exhibit theability to respond to an external stimulus by changing one or more oftheir properties (e.g. elastic modulus, crystal structure, or the like).

The suspended body may be any device that utilizes spatial positioningsuch as a door in an automobile or a residential building; the hood ortrunk of a automobile; the jaws of a vice or a press; the platens onmachine tools such as injection molding machines, compression moldingmachines; arbors and chucks on lathes and drilling machines, or thelike. The supporting body can comprise a door frame, an automobileframe, a aircraft frame, a ship frame, or the like. The suspended bodyis generally movable and can be displaced with respect to the supportingbody, which generally occupies a fixed position. The suspended body canbe opened or closed with respect to the supporting body.

In one embodiment, the locking device advantageously increasesresistance on the movement of the strut assembly. This resistanceincreases the resistance to the motion of a suspended body that is inoperative communication with the strut assembly. The devices also permitlocking of the strut assemblies and hence of the suspended body withoutthe use of any power or energy i.e., they are capable of a power-offlocking of the suspended body. The strut assemblies advantageouslypermit locking of the article in an infinite number of positions and canlock the article during any position along its length of travel. Thedevices can advantageously lock the suspended body in any desiredposition either as the suspended body is being opened or closed.

In one embodiment, the positioning or repositioning of the suspendedbody that is in operative communication with the strut assembly isaccomplished by the application of a suitable manual force. In anotherembodiment, the positioning or repositioning of an article that is inoperative communication with the strut assembly is accomplished by useof a motive force such as mechanical energy or electrical energy.Positioning or repositioning is defined as the motion imparted to thearticle by manual force or other motive forces such as mechanicalenergy, electrical energy, or the like. The ability to position and lockan article in a state of equilibrium at one or more desirable pointsalong the length of its travel is termed detent. The strut assembliesthat employ the locking devices have an infinite detent capability andpermit positioning or repositioning of a suspended body that is inoperative communication with the strut assembly at any degree of openingwith the minimal use of force or restraint.

As stated above, the locking devices can comprise components that arelocated inside or outside the strut assembly if desired. In oneembodiment, components of the locking device can be in a supportiverelationship with the housing of the strut assembly. A supportiverelationship as defined herein is indicated to mean that components ofthe locking device are physically supported by the housing. In anotherembodiment, components of the locking device are in a supportiverelationship with a frame that is not in operative communication withthe housing. In yet another embodiment, the locking device can be in asupportive relationship with the piston or to a fixture in operativecommunication with the piston.

The locking devices employ active materials (e.g., shape memorymaterials) that can be activated by applying an activation signal tolock the piston of the strut assembly in a desired position. Shapememory materials generally refer to materials or compositions that havethe ability to remember their original shape, which can subsequently berecalled by applying an external stimulus, i.e., an activation signal.Exemplary shape memory materials suitable for use in the presentdisclosure include shape memory alloys, ferromagnetic shape memoryalloys, shape memory polymers and composites of the foregoing shapememory materials with non-shape memory materials, and combinationscomprising at least one of the foregoing shape memory materials. Inanother embodiment, the class of active materials used in the strutassembly are those that change their shape in proportion to the strengthof the applied field but then return to their original shape upon thediscontinuation of the field. Exemplary active materials in thiscategory are electroactive polymers (dielectric polymers),piezoelectrics, and piezoceramics. Activation signals can employ anelectrical stimulus, a magnetic stimulus, a chemical stimulus, amechanical stimulus, a thermal stimulus, or a combination comprising atleast one of the foregoing stimuli.

FIG. 1 is an exemplary depiction wherein the locking device 11 isfixedly attached to a strut assembly 10 that comprises a housing 2 thatis in slideable or rotary communication with a piston 3. The piston 3comprises a piston head 14 and a piston rod 12. The piston head 14 isfixedly attached to the piston rod 12. The housing 2 contains a fluid 4.The piston head 14 has disposed in it channels 8 that permit the passageof fluid through the piston head 14 as it moves forward and backward inthe housing 2. Seals 6 are circumferentially disposed upon the pistonhead 14 and seal the space between the piston head 14 and the housing 2.The seals 6 are concentric with the piston head 14. Additional seals 6can also be optionally disposed between the piston rod 12 and thehousing 2. The strut assembly 10 is in operative communication with asupporting body 50 (e.g., the body of the vehicle) and is also inoperative communication with a suspended body 60 (e.g., a suspendedmember 60 that swings back and forth such as a door). The supportingbody 50 and the suspended body 60 are disposed at opposing ends of thestrut assembly 10. While FIG. 1 depicts the suspended body 60 as beingcontacted by the housing 2 and the supporting body 50 as being contactedby the piston rod 12, it is envisioned that the suspended body 60 can becontacted by the piston rod 12 while the supporting body can becontacted by the housing 2. Exemplary moveable parts of the strutassembly 10 are the piston 3, the housing 2, or any other componentssuch as worm wheels, gears, pinions, or the like, that are in operativecommunication with the piston and/or the housing and which facilitatethe displacement of the suspended body 60.

The locking device comprises a tilt washer 22 that is in operativecommunication with an active element 20 that comprises an activematerial. The tilt washer 22 is disposed outside the housing 2, but canbe disposed internally if desired. In one embodiment, the tilt washer 22may be in pivotable communication with the housing 2 or with anotherdesired frame that may or may not be in operative communication with thestrut assembly 10.

As can be seen in the FIG. 2, which depicts a side view and a front viewof the locking device 11, the tilt washer 22 comprises a first end thatpivots about a hinge 24 that is affixed to the outer surface of thehousing 2 and a second end that is in slideable communication with anouter surface of the housing 2. In one embodiment, the second end of thehinge may be in slideable communication with the outer surface of thehousing 2, via a guide (not shown). In another embodiment, the hinge 24comprises an elastomeric material that flexes to accommodate the changein slope of the tilt washer that is desirable to lock or unlock thepiston rod 12. The tilt washer 22 also has disposed in it a hole 26through which passes the piston rod 12. The smallest diameter of thehole 26 is larger than the diameter of the piston rod 12. When thesuspended body 60 (not shown) is displaced with respect to thesupporting body 50 (not shown), the piston rod 12 travels back and forth(reciprocates) through the hole 26 in the tilt washer 22 until a surfaceof the tilt washer 22 contacts the piston rod 12 and exerts axialfriction on the piston rod 12 or otherwise produces mechanicalinterference that resists the motion of the piston rod.

As can be seen in the FIG. 2, the tilt washer has a geometry effectiveto contact the piston rod 12 upon activation of the active element 20.The tilt washer 22 can have any suitable geometry depending upon theselected application and space restrictions. A portion of the tiltwasher 22 is in operative communication with the active element 20,which upon activation promotes displacement of the tilt washer 22. Theactive element 20 is disposed between the tilt washer 22 and an activeelement support panel 28. In its default position, the tilt washercontacts the piston rod 12 and locks it. Activation of the activeelement 20 can displace the tilt washer 22 such that the surface of thehole 26 no longer contacts the piston rod 12. This reduces the axialfriction and permits the displacement of the piston rod and hence of thesuspended body 60. In one embodiment, the active element 20 can displacethe tilt washer 22 against a restoring force (e.g., produced by theelastic deformation of the tilt washer, or produced by an externalbiasing spring, or the like) to displace the tilt washer from itsdefault position.

FIG. 3 depicts one manner of operating the locking device 11. FIG. 3( a)is an exemplary depiction showing the tilt washer 22 in its defaultposition. In its default position, which will now be referred to as itsfirst position, the tilt washer 22 acts as a normally engaged brake andresists the motion of the piston rod 12. The piston rod 12 can be heldin this position even after the activating signal to the active elementis removed or discontinued. This is referred to as a power-off hold.

When it is desired to once again displace the suspended body 60, anactivating signal is applied to the active element 20, therebydisplacing the tilt washer 22 to a second position. In the secondposition, the tilt washer 22 does not contact the piston rod 12 and doesnot exert any axial frictional on the piston rod 12. Hence the pistonrod 12 can be freely displaced. When it is desired to lock the suspendedbody 60 once again, the active element 20 is once again deactivated. Therestoring force of the hinge 24 or that or a restoring or biasing spring(not shown) can be used to restore the tilt washer 22 to its originalposition thereby locking the piston rod 12.

As noted above, the active element 20 comprises an active material(e.g., shape memory material). In one embodiment, the active element 20consists essentially of the active material. In another embodiment, theactive element 20 can comprise active materials and or passive (i.e.,non-active) materials. Passive materials are those that do not recovertheir original shape after the application of an external stimulus. Theactive element 20 can comprise a single active element or multipleactive elements. When more than one active element is used, they can bearranged in series or in parallel or combinations thereof.

In one embodiment, the active element 20 may be part of a motor that isused to actuate the tilt washer 20. Examples of such motors are electricstepper motors, inchworms, piezoelectric inchworms, ultrasonic motors,electrohydrostatic actuators, nanomotion piezoelectric motors, compacthybrid actuator devices (CHAD), or the like, or a combination comprisingat least one of the foregoing motors.

For convenience and by way of example, reference herein will be made toshape memory alloys. An exemplary active material is a shape memoryalloy. Shape memory alloys (SMA's) generally refer to a group ofmetallic materials that demonstrate the ability to return to somepreviously defined shape or size when subjected to an appropriatethermal stimulus. Shape memory alloys are capable of undergoing phasetransitions in which their elastic modulus, yield strength, and shapeorientation are altered as a function of temperature. Generally, in thelow temperature, or martensite phase, shape memory alloys can beplastically deformed and upon exposure to some higher temperature willtransform to an austenite phase, or parent phase, returning to theirshape prior to the deformation. Materials that exhibit this shape memoryeffect only upon heating are referred to as having one-way shape memory.Those materials that also exhibit shape memory upon re-cooling arereferred to as having two-way shape memory behavior.

Shape memory alloys can exhibit a one-way shape memory effect, anintrinsic two-way effect, or an extrinsic two-way shape memory. Annealedshape memory alloys generally exhibit the one-way shape memory effect.Sufficient heating subsequent to low-temperature deformation of theshape memory material will induce the martensite to austenite typetransition, and the material will recover the original, annealed shape.Hence, one-way shape memory effects are only observed upon heating.

Intrinsic two-way shape memory alloys are characterized by a shapetransition both upon heating from the martensite phase to the austenitephase, as well as an additional shape transition upon cooling from theaustenite phase back to the martensite phase. In contrast, activeconnector elements that exhibit the extrinsic two-way shape memoryeffects are composite or multi-component materials that combine a shapememory alloy composition that exhibits a one-way effect with anotherelement that provides a restoring force to return the first plateanother position or to its original position. Active elements thatexhibit an intrinsic one-way shape memory effect are fabricated from ashape memory alloy composition that will cause the active elements toautomatically reform themselves as a result of the above noted phasetransformations. Intrinsic two-way shape memory behavior must be inducedin the shape memory material through thermo-mechanical processing. Suchprocedures include extreme deformation of the material while in themartensite phase, heating-cooling under constraint or load, or surfacemodification such as laser annealing, polishing, or shot-peening. Oncethe material has been trained to exhibit the two-way shape memoryeffect, the shape change between the low and high temperature states isgenerally reversible and persists through a high number of thermalcycles.

The temperature at which the shape memory alloy remembers its hightemperature form when heated can be adjusted by slight changes in thecomposition of the alloy and through heat treatment. In nickel-titaniumshape memory alloys, for instance, it can be changed from above about100° C. to below about −100° C. The shape recovery process occurs over arange of just a few degrees and the start or finish of thetransformation can be controlled to within a degree or two depending onthe alloy composition.

Suitable shape memory alloy materials for fabricating the activeelements include nickel-titanium based alloys, indium-titanium basedalloys, nickel-aluminum based alloys, nickel-gallium based alloys,copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys,copper-gold, and copper-tin alloys), gold-cadmium based alloys,silver-cadmium based alloys, indium-cadmium based alloys,manganese-copper based alloys, iron-platinum based alloys,iron-palladium based alloys, or the like, or a combination comprising atleast one of the foregoing shape memory alloys. The alloys can bebinary, ternary, or any higher order so long as the alloy compositionexhibits a shape memory effect, e.g., change in shape orientation,changes in yield strength, and/or flexural modulus properties, dampingcapacity, and the like.

The thermal activation signal may be applied to the shape memory alloyin various ways. It is generally desirable for the thermal activationsignal to promote a change in the temperature of the shape memory alloyto a temperature greater than or equal to its austenitic transitiontemperature. Suitable examples of such thermal activation signals thatcan promote a change in temperature are the use of steam, hot oil,resistive electrical heating, or the like, or a combination comprisingat least one of the foregoing signals. A preferred thermal activationsignal is one derived from resistive electrical heating.

The active element 20 may also be an electrically active polymer.Electrically active polymers are also commonly known as electroactivepolymers (EAP's). The key design feature of devices based on thesematerials is the use of compliant electrodes that enable polymer filmsto expand or contract in the in-plane directions in response to appliedelectric fields or mechanical stresses. When EAP's are used as theactive element 20, strains of greater than or equal to about 100%,pressures greater than or equal to about 50 kilograms/square centimeter(kg/cm²) can be developed in response to an applied voltage. The goodelectromechanical response of these materials, as well as othercharacteristics such as good environmental tolerance and long-termdurability, make them suitable for active elements under a variety ofmanufacturing conditions. EAP's are suitable for use as an activeelement in many strut assembly 10 configurations.

Electroactive polymer coatings used in strut assembly 10 may be selectedbased on one or more material properties such as a high electricalbreakdown strength, a low modulus of elasticity-(for large or smalldeformations), a high dielectric constant, and the like. In oneembodiment, a polymer is selected such that is has an elastic modulus atmost about 100 MPa. In another embodiment, the polymer is selected suchthat is has a maximum actuation pressure between about 0.05 MPa andabout 10 MPa, and preferably between about 0.3 MPa and about 3 MPa. Inanother embodiment, the polymer is selected such that is has adielectric constant between about 2 and about 20, and preferably betweenabout 2.5 and about 12. The present disclosure is not intended to belimited to these ranges. Ideally, materials with a higher dielectricconstant than the ranges given above would be desirable if the materialshad both a high dielectric constant and a high dielectric strength. Inmany cases, electroactive polymers may be fabricated and implemented asthin films. Thicknesses suitable for these thin films may be below 50micrometers.

As electroactive polymers may deflect at high strains, electrodesattached to the polymers should also deflect without compromisingmechanical or electrical performance. Generally, electrodes suitable foruse may be of any shape and material provided that they are able tosupply a suitable voltage to, or receive a suitable voltage from, anelectroactive polymer. The voltage may be either constant or varyingover time. In one embodiment, the electrodes adhere to a surface of thepolymer. Electrodes adhering to the polymer are preferably compliant andconform to the changing shape of the polymer. Correspondingly, thepresent disclosure may include compliant electrodes that conform to theshape of an electroactive polymer to which they are attached. Theelectrodes may be only applied to a portion of an electroactive polymerand define an active area according to their geometry. Various types ofelectrodes suitable for use with the present disclosure includestructured electrodes comprising metal traces and charge distributionlayers, textured electrodes comprising varying out of plane dimensions,conductive greases such as carbon greases or silver greases, colloidalsuspensions, high aspect ratio conductive materials such as carbonfibrils and carbon nanotubes, and mixtures of ionically conductivematerials.

Materials used for electrodes may vary. Suitable materials used in anelectrode may include graphite, carbon black, colloidal suspensions,thin metals including silver and gold, silver filled and carbon filledgels and polymers, and ionically or electronically conductive polymers.It is understood that certain electrode materials may work well withparticular polymers and may not work as well for others. By way ofexample, carbon fibrils work well with acrylic elastomer polymers whilenot as well with silicone polymers.

The electroactive polymers (EAP's) used herein, are generally conjugatedpolymers. Suitable examples of EAP's are poly(aniline), substitutedpoly(aniline)s, polycarbazoles, substituted polycarbazoles, polyindoles,poly(pyrrole)s, substituted poly(pyrrole)s, poly(thiophene)s,substituted poly(thiophene)s, poly(acetylene)s, poly(ethylenedioxythiophene)s, poly(ethylenedioxypyrrole)s, poly(p-phenylenevinylene)s, or the like, or combinations comprising at least one of theforegoing EAP's. Blends or copolymers or composites of the foregoingEAP's may also be used. Similarly blends or copolymers or composites ofan EAP with an EAP precursor may also be used.

The actuator element 20 used in the customizable strut assembly 10 mayalso comprise a piezoelectric material. Also, in certain embodiments,the piezoelectric material may be configured for providing rapiddeployment. As used herein, the term “piezoelectric” is used to describea material that mechanically deforms (changes shape and/or size) when avoltage potential is applied, or conversely, generates an electricalcharge when mechanically deformed. As piezoelectric actuators have asmall output stroke, they are usually coupled with a transmission (e.g.a compliant mechanism) that serves to amplify the output stroke at theexpense of a reduction in the output force. As an example, apiezoelectric material is disposed on strips of a flexible metal sheet.The piezo actuators are coupled to the sheet in a manner that causesbending or unbending of the sheet when the actuators are activated. Theability of the bending mode of deformation in a flexible shell toamplify small axial strains into larger rotary displacements is used toadvantage. The strips can be unimorph or bimorph. Preferably, the stripsare bimorph, because bimorphs generally exhibit more displacement thanunimorphs.

In contrast to the unimorph piezoelectric device, a bimorph deviceincludes an intermediate flexible metal foil sandwiched between twopiezoelectric elements. Bimorphs exhibit more displacement thanunimorphs because under the applied voltage one ceramic element willcontract while the other expands. Bimorphs can exhibit strains up toabout 20%, but similar to unimorphs, generally cannot sustain high loadsrelative to the overall dimensions of the unimorph structure.

Suitable piezoelectric materials include inorganic compounds, organiccompounds, and metals. With regard to organic materials, all of thepolymeric materials with non-centrosymmetric structure and large dipolemoment group(s) on the main chain or on the side-chain, or on bothchains within the molecules, can be used as candidates for thepiezoelectric film. Examples of suitable polymers include, for example,but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), polyS-119 (poly(vinylamine)backbone azo chromophore), and their derivatives;polyfluorocarbons, including polyvinylidene fluoride (“PVDF”), itsco-polymer vinylidene fluoride (“VDF”), trifluoroethylene (TrFE), andtheir derivatives; polychlorocarbons, including poly(vinyl chloride)(“PVC”), polyvinylidene chloride (“PVC2”), and their derivatives;polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids,including poly(methacrylic acid (“PMA”), and their derivatives;polyureas, and their derivatives; polyurethanes (“PUE”), and theirderivatives; bio-polymer molecules such as poly-L-lactic acids and theirderivatives, and membrane proteins, as well as phosphate bio-molecules;polyanilines and their derivatives, and all of the derivatives oftetramines; polyimides, polyetherimides (“PEI”), and their derivatives;all of the membrane polymers; poly(N-vinyl pyrrolidone) (“PVP”)homopolymer, and its derivatives, and random PVP-co-vinyl acetate(“PVAc”) copolymers; and all of the aromatic polymers with dipole momentgroups in the main-chain or side-chains, or in both the main-chain andthe side-chains, and mixtures thereof.

Further, piezoelectric materials can include Pt, Pd, Ni, Ti, Cr, Fe, Ag,Au, Cu, and metal alloys and mixtures thereof. These piezoelectricmaterials can also include, for example, metal oxide such as SiO₂,Al₂O₃, ZrO₂, TiO₂, SrTiO₃, PbTiO₃, BaTiO₃, FeO₃, Fe₃O₄, ZnO, andmixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS,GaAs, AgCaSe₂, ZnSe, GaP, InP, ZnS, and mixtures thereof.

Shape memory polymers (SMPs) can also be used in the locking and detentmechanisms. Most commonly, they can be used to provide means forpower-off position holding. Generally, SMP's are co-polymers comprisedof at least two different units which may be described as definingdifferent segments within the co-polymer, each segment contributingdifferently to the elastic modulus properties and thermal transitiontemperatures of the material. The term “segment” refers to a block,graft, or sequence of the same or similar monomer or oligomer units thatare copolymerized with a different segment to form a continuouscrosslinked-interpenetrating network of these segments.

These segments may be a combination of crystalline or amorphousmaterials and therefore may be generally classified as a hard segment(s)or a soft segment(s), wherein the hard segment generally has a higherglass transition temperature (Tg) or melting point than the softsegment. Each segment then contributes to the overall elastic modulusproperties of the SMP and the thermal transitions thereof. When multiplesegments are used, multiple thermal transition temperatures may beobserved, wherein the thermal transition temperatures of the copolymermay be approximated as weighted averages of the thermal transitiontemperatures of its comprising segments. The previously defined orpermanent shape of the SMP can be set by molding the polymer at atemperature higher than the highest thermal transition temperature forthe shape memory polymer or its melting point, followed by cooling belowthat thermal transition temperature.

In practice, the SMP's are alternated between one of at least two shapeorientations such that at least one orientation will provide a sizereduction or shape change relative to the other orientation(s) when anappropriate thermal signal is provided. To set a permanent shape, theSMP must be at about or above its melting point or highest transitiontemperature (also termed “last” transition temperature). The SMP's areshaped at this temperature by blow molding, injection molding, vacuumforming, or the like, or shaped with an applied force followed bycooling to set the permanent shape. The temperature to set the permanentshape is about 40° C. to about 300° C. After expansion, the permanentshape is regained when the applied force is removed, and the SMP formeddevice is again brought to or above the highest or last transitiontemperature of the SMP. The Tg of the SMP can be chosen for a particularapplication by modifying the structure and composition of the polymer.Transition temperatures of suitable SMPs generally range from about −63°C. to above about 160° C.

The temperature desired for permanent shape recovery can be set at anytemperature of about −63° C. and about 160° C., or above. Engineeringthe composition and structure of the polymer itself can allow for thechoice of a particular temperature for a desired application. Apreferred temperature for shape recovery is greater than or equal toabout −30° C., more preferably greater than or equal to about 20° C.,and most preferably a temperature greater than or equal to about 70° C.Also, a preferred temperature for shape recovery is less than or equalto about 250° C., more preferably less than or equal to about 200° C.,and most preferably less than or equal to about 180° C.

The shape memory polymers used in the active device can bethermoplastics, interpenetrating networks, semi-interpenetratingnetworks, or mixed networks. The polymers can be a single polymer or ablend of polymers. Polymers can be linear, branched, thermoplasticelastomers with side chains or any kind of dendritic structuralelements. In one embodiment the shape memory polymer can be a blockcopolymer, a graft copolymer, a random copolymer or a blend of a polymerwith a copolymer.

Stimuli causing shape change can be temperature, ionic change, pH,light, electric field, magnetic field or ultrasound. Suitable polymercomponents to form a shape memory polymer include polyphosphazenes,polyacrylics, polyalkyds, polystyrenes, polyesters, polyaramides,polyamideimides, polyarylates, polyarylsulfones, polyethersulfones,polyphenylene sulfides, polysulfones, polyimides, polyetherimides,polytetrafluoroethylenes, polyetherketones, polyether etherketones,polyether ketone ketones, polybenzoxazoles, polyoxadiazoles,polybenzothiazinophenothiazines, polybenzothiazoles,polypyrazinoquinoxalines, polypyromellitimides, polyquinoxalines,polybenzimidazoles, polyoxindoles, polyoxoisoindolines,polydioxoisoindolines, polytriazines, polypyridazines, polypiperazines,polypyridines, polypiperidines, polytriazoles, polypyrazoles,polycarboranes, polyoxabicyclononanes, polydibenzofurans,polyphthalides, polyacetals, polyanhydrides, polyvinyl ethers, polyvinylthioethers, polyvinyl alcohols, polyvinyl ketones, polyvinyl halides,polyvinyl nitriles, polyvinyl esters, polysulfonates, polysulfides,polythioesters, polysulfones, polysulfonamides, polyureas,polyphosphazenes, polysilazanes, poly(vinyl alcohols), polyamides,polyester amides, poly(amino acid)s, polyanhydrides, polycarbonates,polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols,polyalkylene oxides, polyalkylene terephthalates, polyortho esters,polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters,polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers,polyether amides, polyether esters, and copolymers thereof. Examples ofsuitable polyacrylates include poly(methyl methacrylate), poly(ethylmethacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate),poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene,polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinatedpolybutylene, poly(octadecyl vinyl ether), ethylene vinyl acetate,polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate),polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (blockcopolymer), poly(caprolactone) dimethacrylate-n-butyl acrylate,poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride,urethane/butadiene copolymers, polyurethane block copolymers,styrene-butadiene-styrene block copolymers, and the like. The polymerused to form the various segments in the SMPs described above are eithercommercially available or can be synthesized using routine chemistry.

The SMP's may be advantageously reinforced with fillers. Suitablefillers may exist in the form of whiskers, needles, rods, tubes,strands, elongated platelets, lamellar platelets, ellipsoids, microfibers, nanofibers and nanotubes, elongated fullerenes, and the like.

FIGS. 4 through 7 depict exemplary embodiments of another locking device11 that is disposed outside the housing 2. While the examples depictedin the FIG. 4 display the locking mechanism as being deployed outsidethe housing 2, it can be located inside the housing 2 as well. FIG. 4shows different positions where the locking device 11 can be deployed.

With reference now to the FIG. 5, the locking device 11 comprises asleeve 32 that can be elastically deformed by an active element 20. Inone embodiment, the sleeve 32 contacts the piston rod 12 in order toprevent the piston rod from being displaced further along its line oftravel. The sleeve 32 can also contact the housing 2 in order to preventthe housing from being displaced further along its line of travel. It isgenerally desirable for the sleeve 32 to contact that portion of thestrut assembly 10 that is adapted to permit the displacement of thesuspended body 60. As shown in the FIG. 5, the sleeve 32 is in operativecommunication with the active element 20, which upon activation canradially compress the sleeve 32 to contact the outer surface of thehousing 2 since in this exemplary embodiment, the housing is fixedlyattached to the suspended body 60. The sleeve 32 is also in operativecommunication with optional return springs 30, whose spring constant canbe adjusted to vary the resistance imparted by the sleeve to the pistonrod. The optional return springs are fixedly attached to supports 29that are affixed to either the housing 2 or the suspended body 60.

In one embodiment, the sleeve 32 can comprise a lining or a coating (notshown) on the surface that contacts the housing 2. The lining can beused to modify the frictional properties of the inner surface of thesleeve or on the corresponding surface of the piston rod or the housing.An elastic deformation of the sleeve 32 can be used to vary thefrictional force between the sleeve 32 and the housing 2, by varying thearea of contact between the sleeve 32 and the housing 2, by varying thecontact pressure (magnitude and/or distribution) between the sleeve 32and the housing 2, or by a combination thereof. In one embodiment, thedefault condition of the sleeve 32 can be selected (e.g., by design, byadjusting the tension in the return springs 30, or the like) to impart adesired level of frictional resistance to the motion of the housing 2.During the operation of the suspended body 60, the elastic deformationof the sleeve 32 and hence the frictional resistance to the motion ofhousing 2, can be adjusted by the active element 20.

In the default condition of the locking device 11, the sleeve 32 doesnot contact the housing 2. In this condition the active element 20 isconsidered to be in a strain-free configuration since it has no residualstress. The active element 20 can be actuated by passing an electriccurrent through it to induce a martensitic to austenitic phasetransition in the shape memory material. This transformation isassociated with a large strain recovery, and a correspondingly largerecovery force is exerted if the strain recovery is resisted.

Upon activation, the active element 20 applies a compressive radialforce to the sleeve 32. The recovery force deforms the sleeve 32 toincrease the contact area and/or the contact pressure, therebyincreasing the frictional resistance to the movement of the housing 2.The magnitude of the actuation force can be controlled by either theforce applied by the return springs 30 or by the magnitude of theactivation that the active element 20 is subjected to. The increasedfrictional resistance imparted by the sleeve 32 to the housing 2 iseffective as long as the element active element 20 remains actuated.

When the current flowing through the active element 20 is switched off,the shape memory material transforms back to the martensitic phase, andthe sleeve 32 is restored to its default condition because of theelastic recovery of the sleeve 32 as well as because of the restoringforce applied by the return spring 30. The recovery process results inpseudo-plastic straining of the martensitic phase shape memory materialelement, and hence the system is restored to its initial configuration.

FIG. 6 reflects another variation, wherein the positions of the activeelement 20 are switched with those of the return spring 30. Here theelastic force of the sleeve counteracts the compressive force exerted bythe return spring 30. The active element 20 can be configured uponactivation to assist and/or resist the compressive forces of the returnspring 30.

FIG. 7 shows yet another variation of the locking device 11 in which theactive element 20 is circumferentially disposed around the sleeve 32 andin intimate contact with it. The active element 20 can cover the entiresleeve 32 or only a portion of the sleeve 32. In an exemplary embodimentwhere the active element is made from a shape memory alloy, the activeelement 20 is disposed around the sleeve when the shape memory alloymaterial is in its martensitic phase. The sleeve is therefore forcedinto its most compact form by extraneous forces acting during theassembly of the locking device.

When these forces are removed, the elastic energy stored in the deformedsleeve 32 will try to recover the original (or unstressed) configurationof the sleeve 32. In this process the shape memory alloy materialwrapping will get pseudo-plastically strained. The passage of a currentthrough the element will induce a martensite to austenite phasetransformation in the shape memory material, which will then exert asubstantial recovery force in its attempt to recover the unstrainedconfiguration of the shape memory alloy material. The unstrainedconfiguration of the shape memory alloy material corresponds to thecompacted configuration of the sleeve 32. Therefore, the passage of acurrent through the active element will deform the sleeve such as toincrease the contact area and/or pressure between the sleeve 32 and thehousing 2. This enables the assembly comprising the sleeve 32 and shapememory alloy material to function as a frictional brake. When thecurrent is stopped and the shape memory material elements cool down andconvert back to the martensitic phase, the elastic restoring forces fromthe sleeve 32 dominate the force in the shape memory material elementsand thereby restore the starting configuration of the locking device 32.

Many variations of this concept can be implemented. In one exemplaryvariation, the configuration of the active element may be changed into astent-like design, in which the shape memory alloy functions as thesleeve 32 as well as the actuator that controls the configuration of thesleeve. In another variation, other active materials such aselectro-active polymers, piezoelectrics, or the like, may be used inplace of the shape memory alloy.

As noted earlier, the locking device can be disposed inside the housing2. FIG. 8 is a depiction of one exemplary embodiment of the strutassembly 10 wherein the locking device 11 comprises a spring stack 27that is disposed inside the housing 2 between the piston head 14 andplate 29 disposed upon the piston rod 12. The spring stack 27 can bewave springs having washers disposed in between as shown in the FIG. 8.In another embodiment, the spring stack 27 can comprise conic springs,known as Belleville washers. This springs when axially compressed willexpand both radially outward and inward. The spring stack 27 cancomprise a single spring or multiple springs.

The plate 29 is in operative communication with the piston head 14 via anumber of active elements (e.g., studs 34) that are axially disposed andare parallel to the direction of travel of the piston rod 12. The plate29 is in slideable communication with the piston rod 12 and is free tomove along the piston rod 12 until the active elements 20 are activatedby the application of an external stimulus. In an exemplary embodiment,each active element 20 comprises a shape memory alloy. The studs 34 arefixedly attached to the piston head 14. Each stud 34 is in operativecommunication with the plate 29. Upon application of the activationsignal, the studs 34 return to their original shape (memorized shape),which facilitates a displacement of the plate 29 towards the piston head14, thereby applying a compressive force to the spring stack 27 whichcompresses the wave springs causing them to expand radially outwards andcontacting the inner surface of the housing 2. The axial frictionbetween the outer circumference of the wave springs in the spring stack27 and the inner surface of the housing 2 promotes the locking of thestrut assembly 10. As noted above, when the studs 34 comprise a shapememory alloy, they can be activated by the application of heat. Anexemplary method of heating is resistive heating. Other active materialsthat can be employed in the active element are electro-active polymers,piezoelectric materials, or the like.

In yet another exemplary embodiment depicted in FIG. 9, a locking device11 is disposed inside the housing 2. In FIG. 9, the locking devicecomprises a guide 36 having at least a corrugated inner surface. Theguide 36 can have an outer corrugated surface if so desired. In oneembodiment, the guide can be tubular. In another embodiment, the guidecan advantageously employ geometries that are not tubular.

The corrugated surfaces of the guide 36 are comprised of alternatingconvex surfaces 38 and concave surfaces 40 as shown in the FIG. 9. Aconvex surface 38 is defined as one in which the radius of curvature forthe surface is located on the housing side of the guide 36. A concavesurface 40 is defined as one in which the radius of curvature for thesurface is located on the piston rod side of the guide 36. The amplitudeof the waves as well as the wavelength of the waves in the guide 36 canbe varied upon the application. In one embodiment, the guide 36comprises a shape memory alloy layer 42 disposed between two shapememory polymer layers 44, 46 as depicted in the FIG. 9. The shape memorypolymer layers 44, 46 are disposed on opposing surfaces of the shapememory alloy layer 42 and are in intimate contact with the shape memoryalloy layer 42. The shape memory alloy layer 42 has a wave-like shapewhen it is in a stress-free, martensitic condition and this wave-likeshape is imparted to the guide 36. The composition of the shape memoryalloy layer ensures that the guide remains in the martensitic conditionthroughout the operating temperature range of the strut assembly 10. Theshape memory polymer is selected such that its lowest glass transitiontemperature (Tg) is greater than the maximum operating temperature thatthe piston head will experience during the operation of the strutassembly 10. The guide 36 is designed to ensure that at temperaturesbelow Tg, the stiffness of the shape memory polymer matrix determinesthe stiffness of the guide 36, whereas at temperatures above Tg, thestiffness of the shape memory alloy layer determines the stiffness ofthe guide 36.

One or more protrusions 48 disposed on the circumferential surface ofthe piston head 14 contact the inner surface of the guide 36. Theprotrusion 48 is of a size effective to contact the inner surface of theguide 36 as the piston 3 moves back and forth in the housing 2. When theguide 36 is contacted by the protrusion 48, it resists relative motionbetween the piston head 14 and the housing 2. Only by applying a manualforce greater than the resistance to deformation exerted by the guide 36can relative motion between the piston head 14 and the housing 2 occur.When motion occurs between the piston head 14 and the housing 2, theprotrusion 48 deforms the wave-like surface locally as it contacts it.The properties of the guide (e.g., its stiffness) and the geometry ofthe guide (i.e., the amplitude and wavelength of the waves, and thelike) can be varied by the application of a suitable external stimulusi.e., an activating signal. Therefore, the resistance to the motion ofthe suspended member 60 as well as the locking of the suspended member60 can be controlled by varying the properties and the geometry of theguide 36.

When the suspended body 60 is in a locked position, the protrusion 48 isdisposed between two concave surfaces 40 of the tubular guide 36. Asdescribed earlier, relative motion between the piston 3 and the housing2 requires the local deformation of the convex surfaces 38 of thetubular guide 36 as the piston 3 travels back and forth in the housing2. The force effective to induce this deformation, and thus to move thesuspended member 60, depends on the stiffness of the tubular guide 36.If the stiffness of the tubular guide 36 is great enough to resistrelative motion under various applied loads (e.g., weight of thesuspended member 60, wind load, user effort, etc), the tubular guide 36functions as a mechanical stop. When the length of the strut assembly 10has to be changed, the shape memory polymer is heated to a temperatureabove its Tg, whereupon its elastic modulus of the guide 36 decreases.This reduction in the elastic modulus of the guide 36 reduces theresistance of the guide 36 to the motion of the suspended body 60. Thesuspended body 60 can be moved to a new position while the shape memorypolymer is at a temperature greater than or equal to about is lower Tg.When the suspended body 60 reaches its desired position, the heating ofthe shape memory polymer layer is stopped. As the shape memory polymerlayer cools below the Tg, the stiffness of the shape memory polymer andhence the guide increases. This results in locking the suspended body 60in its new position.

When the piston 3 is moved relative to the housing 2 during the periodwhile the shape memory polymer layer is at a temperature greater thanits lowest Tg, the protrusion 48 deforms the guide locally as it travelspast the concave portions of the guide 36. The stiffness of the shapememory alloy layer, which is not reduced by the change in temperature ofthe guide 36, helps restore the deformed regions to their original shapeafter the protrusion 48 has passed by. In one embodiment, the guide 36can retain its original shape by heating the deformed regions to atemperature effective to induce a martensitic to austenitic phasetransformation. The martensitic to austenitic phase transformationfacilitates the restoration of the deformed regions to their originalshape.

The composition of the shape memory alloy layer is chosen such that itcan maintain the integrity of the tubular guide 36 while the shapememory polymer layer undergoes large deformations and providessignificant recovery forces that assist in restoration of the originalconfiguration of the tubular guide 36. As the shape memory alloy hashigh electrical resistivity, the wave-like tubular guide 36 can bereadily heated by passing electric current through the shape memoryalloy elements. Instead of a shape memory alloy, other electricallyconductive materials (e.g. other metals or alloys) can be used in thecomposite.

In yet another exemplary embodiment depicted in the FIGS. 11, 12, 13 and14, the locking device 11 comprises an internal expanding brake disposedinside the housing 2. In one embodiment, depicted in the FIGS. 11 and12, the internal expanding brake can be used as a detent withpotentially an infinite number of stop positions. In another embodimentdepicted in the FIGS. 13 and 14, the internal expanding brake can beused as a detent with a small, finite number of stop positions.

With reference now to the FIGS. 11 and 12, the piston head 14 can bemodified to act as an internal expanding brake that presses against theinner surface of the housing 2 thereby permitting the locking of thestrut assembly 10 in any desired position. An exemplary embodiment ofthis concept is depicted in the FIG. 11. The piston head 14 comprisestwo external portions 51 and a central portion 52 that are disposed onthe piston rod 12. The two external portions 51 and the central portion52 are in operative communication with the piston rod 12. The centralportion 52 of the piston head comprises one or more brake shoes 54 thatare in mechanical communication with the piston rod 12 by elasticmembers 56. The elastic members 56 are disposed between the piston rod12 and the brake shoes 54 and extend radially outwards from the pistonrod 12 to the brake shoes 54.

In one embodiment, as depicted in the FIG. 12, the central portion 52can have three brake shoes. When the elastic members 56 areun-constrained, the effective outer diameter of the piston head 14 dueto the brake shoes 54 is larger than the inner diameter of the housing2. In order to be disposed within the housing 2, the brake shoes 54 areradially compressed and positioned in the housing. Thus, the elasticrestoring force produced by the compression of the elastic membersduring assembly gives rise to a radial force that presses the brakeshoes 54 against the inner surface of the housing 2. This radial forceproduces an axial friction between the brake shoes 54 and the innersurface of the housing 2. As can be seen in the FIGS. 11 and 12, shapememory alloy wires 58 are wound circumferentially around the brake shoes54. When activated, the shape memory alloy elements (e.g. wires) 58facilitate the compression of the elastic members 56, thereby reducingthe axial friction between the brake shoes 54 and the inner surface ofthe housing 2. The restoring force of the elastic members 56 istherefore opposed by the hoop stress induced in the shape memory alloyelement 58.

In one embodiment, in one manner of operating the strut assembly 10depicted in the FIGS. 11 and 12, the brake shoes 54 contact the innersurface of the housing 3 thereby preventing any displacement of thesuspended body 60. The suspended body 60 is therefore locked. In thisdefault position, the shape memory alloy element 58 is in itsmartensitic phase. The elastic force exerted radially outwards by thebrake shoes 54 produces an axial friction with the inner surface of thehousing 3, which facilitates the locking of the strut assembly 10.

If it is desired to displace the suspended body 60, an activating signalis applied to the shape memory element 58. The activation signal, whichis generally in the form of resistive heating promotes a transformationof the shape memory element 58 from the martensitic state to theaustenitic state. This solid-state transformation produces a largerestoring force that attempts to recover the pseudo-elastic straininduced in the wire 58. This restoring force opposes the elastic forceproduced by the elastic members and thus, reduces the radial force,which presses the brake shoes 54 against the inner surface of thehousing 2. Thus by activating the shape memory element 58, a compressiveforce is applied to the brake shoes 54. This compressive force reducesor eliminates the frictional contact between the brake shoes 54 and theinner surface of the housing 2, thereby permitting motion of the piston3 and hence of the suspended member 60.

The design of the piston head 14 and the material, geometry, number andelectrical/mechanical connectivity of the shape memory alloy wires 58can be selected such that the frictional resistance can be varied over awide range e.g., this system can act as an on-off brake, or it canprovide a continuously variable frictional resistance to the motion ofthe piston rod 12 and hence to the suspended member 60. The shape memoryalloy wires can be activated in response to a number of different inputse.g. the user can explicitly select the braking force level, or theactivation can be induced by a change in ambient temperature. Othermeans of actuation, e.g., electroactive polymers, piezoelectricmaterials, or the like may be used instead of the shape memory alloyelements 58.

In another exemplary embodiment, the strut assemblies depicted in theFIGS. 11 and 12 can be used to set a finite number of stops for thepiston 3 and the suspended member 60 as displayed in the FIGS. 13 and14. As depicted in the FIG. 13, two locking rings 62 are used to createthe desired intermediate locking positions for the strut assembly 10.While locking rings 62 are used in the FIG. 13 to function as lockingdevices 11 for the strut assembly 10, it is envisioned that alternatedevices can be utilized as well. Further, while the FIG. 13 depicts twolocking rings, additional locking rings can be added to the housing tocreate additional positions for locking the strut assembly 10.

As depicted in the FIG. 13, the piston head 14 comprises a centralportion 52 that comprises one or more brake shoes 54 connected by theelastic members 56 to the piston rod 12. As noted above, the elasticmembers are of a size effective to permit the brake shoes to exert aradial pressure on the inner surface of the housing 2, when the pistonhead 14 is assembled inside the housing 2. A shape memory alloy element(e.g. one or more wires) is disposed between each brake shoe 54 and thepiston rod 12 and is in operative communication with the brake shoe 54and the piston rod 12. The shape memory elements can be activated tocounteract the elastic force exerted by the elastic members 56 therebycausing a radial retraction of the brake shoes 54. Each brake shoe 54comprises a circumferential groove 64 on the surface that contacts theinner surface of the housing 2. The circumferential groove 64 is of asize effective to that can accommodate the locking ring 62. When thebrake shoes 54 are retracted radially inwards as a result of theactivation of the shape memory alloy elements, the groove in the brakeshoes 54 is disengaged from the locking ring 62. This disengagementpermits motion of the piston 3 and hence of the suspended member 60.

In one embodiment, pertaining to the operation of the strut assembly 10,the suspended member 60 can be displaced towards or away from thesupporting body 50 till the circumferential groove in the brake shoe 54encounters a locking ring 62. When the circumferential groovemechanically engages the locking ring 62, the strut assembly 10 islocked. Alternatively, the piston head 14 can be permitted to by pass aparticular locking ring 62 by activating the shape memory alloy elements58. The piston head 14 can then be permitted to engage with anotherlocking ring 62.

With respect now to the exemplary embodiment depicted in the FIG. 13, afirst locking ring 62 mechanically engages the circumferential grove onthe brake shoe 54 thereby locking the strut assembly 10. In this lockedposition, the shape memory alloy wires 58 are inactive and the brakeshoes 54 are pressed against the locking rings 62 due to the elasticforce exerted by the elastic members 56 which displaces the brake shoes54 in a radially outward direction. The suspended member 60 is thusmechanically locked in position as a result of the mechanical engagementof the groove with the locking ring 62, which can resist attempts tomove the suspended member 60 in either direction.

If the suspended member 60 is to be released from this position, theshape memory alloy elements are activated by heating (e.g., by passingand electrical current through it). The heating of the shape memoryelements promotes a radial compressive force on the elastic member 56,thereby disengaging the groove in the brake shoe 54 from the lockingring 62 and permitting relative motion between the piston head 14 andthe housing 2. The heating of the shape memory alloy elements 58 isdiscontinued when the locking ring 62 no longer engages thecircumferential groove in the brake shoe 54.

As the shape memory alloy wires cool down, their elastic modulusdecreases. The elastic forces in the elastic members can now overcomethe forces exerted by the shape memory alloy elements 58 and the brakeshoes 54 once again move radially outward exerting a radial pressureagainst the inner surface of the housing 2. The piston 3 and hence thesuspended member 60 can now be displaced freely until the piston head 14encounters a second locking ring. Thus, if the suspended member 60 is tobe locked in another intermediate position, the suspended member 60 ismoved until the brake shoe 54 engages the next locking ring 62. On theother hand, if the suspended member 60 is to be moved past the secondlocking ring, the shape memory alloy elements are re-activated until thesecond locking ring is bypassed. Alternatively, activation of the shapememory alloy elements can be maintained as long as the suspended member60 is to be displaced. The activation can be switched off when thesuspended member 60 is to be locked in another desired position.

As noted above, additional locking rings or grooves in brake shoes canbe added to increase the number of intermediate locking positionsavailable to the suspended member 60. This concept can also be combinedwith the embodiments detailed in the FIGS. 9 and 10, where a guide witha corrugated surface is utilized.

In yet another embodiment depicted in the FIG. 15, the resistance tofluid flow across the piston head 14 can be used to provide resistanceto the displacement of the suspended member 60. The displacement of thefluid across the piston head 14 gives rise to a hydrodynamic resistancethat can be used to control the relative motion of the piston 3 withrespect to the housing 2. This resistance is dependent on the effectiveviscosity of the fluid among other things. Therefore, varying theeffective viscosity of the fluid 4 by an external stimulus enablescontrol over the motion of the suspended body 60. In one embodiment, thefluid 4 can be an electrorheological fluid or a magnetorheologicalfluid.

The term magnetorheological fluid encompasses magnetorheological fluids,ferrofluids, colloidal magnetic fluids, and the like. Magnetorheological(MR) fluids and elastomers are known as “smart” materials whoserheological properties can rapidly change upon application of a magneticfield. MR fluids are suspensions of micrometer-sized, magneticallypolarizable particles in oil or other liquids. When a MR fluid isexposed to a magnetic field, the normally randomly oriented particlesform chains of particles in the direction of the magnetic field lines.The particle chains increase the apparent viscosity (flow resistance) ofthe fluid. The stiffness of the structure is accomplished by changingthe shear and compression/tension modulii of the MR fluid by varying thestrength of the applied magnetic field. The MR fluids typically developstructure when exposed to a magnetic field in as little as a fewmilliseconds. Discontinuing the exposure of the MR fluid to the magneticfield reverses the process and the fluid returns to a lower viscositystate.

Suitable magnetorheological fluids include ferromagnetic or paramagneticparticles dispersed in a carrier fluid. Suitable particles include iron;iron alloys, such as those including aluminum, silicon, cobalt, nickel,vanadium, molybdenum, chromium, tungsten, manganese and/or copper; ironoxides, including Fe2O3 and Fe3O4; iron nitride; iron carbide; carbonyliron; nickel and alloys of nickel; cobalt and alloys of cobalt; chromiumdioxide; stainless steel; silicon steel; or the like, or a combinationcomprising at least one of the foregoing particles. Examples of suitableiron particles include straight iron powders, reduced iron powders, ironoxide powder/straight iron powder mixtures and iron oxide powder/reducediron powder mixtures. A preferred magnetic-responsive particulate iscarbonyl iron, preferably, reduced carbonyl iron.

The particle size should be selected so that the particles exhibitmulti-domain characteristics when subjected to a magnetic field.Diameter sizes for the particles can be less than or equal to about1,000 micrometers, with less than or equal to about 500 micrometerspreferred, and less than or equal to about 100 micrometers morepreferred. Also preferred is a particle diameter of greater than orequal to about 0.1 micrometer, with greater than or equal to about 0.5more preferred, and greater than or equal to about 10 micrometerespecially preferred. The particles are preferably present in an amountbetween about 5.0 and about 60 percent by volume of the totalcomposition.

Suitable carrier fluids include organic liquids, especially non-polarorganic liquids. Examples include, but are not limited to, siliconeoils; mineral oils; paraffin oils; silicone copolymers; white oils;hydraulic oils; transformer oils; halogenated organic liquids, such aschlorinated hydrocarbons, halogenated paraffins, perfluorinatedpolyethers and fluorinated hydrocarbons; diesters; polyoxyalkylenes;fluorinated silicones; cyanoalkyl siloxanes; glycols; synthetichydrocarbon oils, including both unsaturated and saturated; andcombinations comprising at least one of the foregoing fluids.

The viscosity of the carrier component can be less than or equal toabout 100,000 centipoise, with less than or equal to about 10,000centipoise preferred, and less than or equal to about 1,000 centipoisemore preferred. Also preferred is a viscosity of greater than or equalto about 1 centipoise, with greater than or equal to about 250centipoise preferred, and greater than or equal to about 500 centipoiseespecially preferred.

Aqueous carrier fluids may also be used, especially those comprisinghydrophilic mineral clays such as bentonite and hectorite. The aqueouscarrier fluid may comprise water or water comprising a small amount ofpolar, water-miscible organic solvents such as methanol, ethanol,propanol, dimethyl sulfoxide, dimethyl formamide, ethylene carbonate,propylene carbonate, acetone, tetrahydrofuran, diethyl ether, ethyleneglycol, propylene glycol, and the like. The amount of polar organicsolvents is less than or equal to about 5.0% by volume of the total MRfluid, and preferably less than or equal to about 3.0%. Also, the amountof polar organic solvents is preferably greater than or equal to about0.1%, and more preferably greater than or equal to about 1.0% by volumeof the total MR fluid. The pH of the aqueous carrier fluid is preferablyless than or equal to about 13, and preferably less than or equal toabout 9.0. Also, the pH of the aqueous carrier fluid is greater than orequal to about 5.0, and preferably greater than or equal to about 8.0.

Natural or synthetic bentonite or hectorite may be used. The amount ofbentonite or hectorite in the MR fluid is less than or equal to about 10percent by weight of the total MR fluid, preferably less than or equalto about 8.0 percent by weight, and more preferably less than or equalto about 6.0 percent by weight. Preferably, the bentonite or hectoriteis present in greater than or equal to about 0.1 percent by weight, morepreferably greater than or equal to about 1.0 percent by weight, andespecially preferred greater than or equal to about 2.0 percent byweight of the total MR fluid. Optional components in the MR fluidinclude clays, organoclays, carboxylate soaps, dispersants, corrosioninhibitors, lubricants, extreme pressure anti-wear additives,antioxidants, thixotropic agents and conventional suspension agents.Carboxylate soaps include ferrous oleate, ferrous naphthenate, ferrousstearate, aluminum di- and tri-stearate, lithium stearate, calciumstearate, zinc stearate and sodium stearate, and surfactants such assulfonates, phosphate esters, stearic acid, glycerol monooleate,sorbitan sesquioleate, laurates, fatty acids, fatty alcohols,fluoroaliphatic polymeric esters, and titanate, aluminate and zirconatecoupling agents and the like. Polyalkylene diols, such as polyethyleneglycol, and partially esterified polyols can also be included.

The activation device can be configured to deliver an activation signalto the active elements, wherein the activation signal comprises amagnetic signal. The magnetic signal is a magnetic field. The magneticfield may be generated by a permanent magnet, an electromagnet, orcombinations comprising at least one of the foregoing. The strength anddirection of the magnetic field is dependent on the particular materialemployed for fabricating the hook element, as well as amounts andlocation of the material on the hook. Suitable magnetic flux densitiesfor the active elements comprised of MR fluids or elastomers range fromgreater than about 0 to about 1 Tesla. Suitable magnetic flux densitiesfor the hook elements comprised of magnetic materials range from greaterthan about 0 to about 1 Tesla.

Electrorheological fluids are most commonly colloidal suspensions offine particles in non-conducting fluids. Under an applied electricfield, electrorheological fluids form fibrous structures that areparallel to the applied field and can increase in viscosity by a factorof up to 10⁵. The change in viscosity is generally proportional to theapplied potential. ER fluids are made by suspending particles in aliquid whose dielectric constant or conductivity is mismatched in orderto create dipole particle interactions in the presence of an alternatingcurrent (ac) or direct current (dc) electric field.

With reference now to the FIG. 15, optional circular permanent magnets66 are disposed around the flow channels 8 in the piston head 14. Theoptional circular permanent magnets 66 produce a magnetic field B2 thatinfluences the viscosity of the fluid 4 in the channels 8.Circumferentially disposed around the permanent magnets areelectromagnets 68 that are used to apply a second magnetic field B1 thatopposes B2. In one embodiment, the permanent magnet 66 and theelectromagnet 68 are concentric. In another embodiment, the permanentmagnet 66 and the electromagnet 68 are coaxial but not concentric, i.e.,they share the same axis, but are not concentric. The strength of themagnetic field B2 is fixed, while that of B1 can be varied bycontrolling the electric current flowing through the electromagnets 68.The effective magnetic field acting on the fluid 4 as it traverses theflow channels 8 is therefore the difference in strengths between B1 andB2 and this difference can be controlled by varying the current throughthe electromagnet 68. The difference in strength between B1 and B2determines the viscosity of the fluid in the flow channels. Thus thehydrodynamic resistance to the strut motion can be adjusted on demand byvarying the current flowing through the electromagnet.

In one embodiment, by excluding the permanent magnet and using only anelectromagnet, the hydrodynamic resistance can only be increased bycontrolling the electric current through the electromagnet 68. Inanother embodiment, the use of two opposing electromagnets permits atwo-way control over the hydrodynamic resistance, i.e., it can beincrease or decreased. In yet another embodiment, by employing only apermanent magnet adjacent to the channel, the magnetic circuit thatdetermines the field in the flow channels can be changed (e.g., byactivating an SMA actuator) thereby controlling the effective fieldstrength in the flow channel, and consequently the resistance torelative motion between the cylinder and the piston.

In yet another exemplary embodiment, a pivot detent locking device thatemploys rotary motion to facilitate the locking of a suspended body 60is depicted in FIGS. 16 through 19.

The locking device 11 comprises a multi-bar linkage that comprises along arm 72 and a short arm 70 rotatably disposed about a pivot point,as depicted in FIGS. 16 and 17. FIG. 16 provides a front view of thelocking device 11, while FIG. 17 provides a rear view of the device 11.The short arm 70 of the locking device 11 is constrained on the pivotpin 76 between a ball disk 78 and the long arm 72. Affixed to theopposing surface of the long arm 72 is the cylindrical housing 74, whichcomprises an actuator 92. The actuator 92 is in operative communicationwith a piston 94.

FIG. 18 is a section view of the pivot detent-locking device 11 in itsnormally locked position. Locking is accomplished by using a seriesballs 82 trapped in the ball disk 78 and engaged in detents 84 disposedin the short arm 70. The ball disk 78 is attached to the pivot pin 76,which is connected to a piston 94, having a seal 96 and contained thecylindrical housing 74. The piston 94 can move axially along thecenterline of the cylindrical housing 74. A spring 88 constrainedbetween the piston 94 and the long arm provides the reaction/biasingforce necessary for the pivot pin to move the balls 82 trapped in theball disk 78 to engage the detents 84 in the short arm 70, thus lockingthe short arm 70 relative to the long arm 72 and prohibiting rotation.

Also contained in the cylindrical housing 74 is an actuator 92, whichacts on the opposite side of the piston 94 from the spring 88. On theopposing side of the actuator 92 is a heater constrained by a backingplate and located in the end of the cylindrical housing 74. The heateris also connected to a power source (not shown).

Upon receiving a signal from the control circuit (not shown), the powersource 80 provides energy to the actuator 92, in this case a shapememory polymer or a shape memory alloy, causing the actuator 92 toexpand. FIG. 19 (section view) shows the detent-locking device 11 in itsunlocked position. As the actuator 92 expands, the piston 94 moves thepivot pin 76 axially forcing the ball disk 78 to move. As the ball disk78 moves, the balls 82 trapped in the ball disk are free to move axiallyout of the detents 84 in the short arm 70. As the clearance between theballs 82 and the detents 84 increases the short arm 70 is free to rotateabout the pivot pin 76, thus allowing the short arms 70 to rotate freelyrelative to the long arms 72.

Upon receiving a signal from the control circuit, the power source 80will remove the energy provided to the actuator 92. The actuator 92 willthen start to cool and biased by the spring 88 will contract to itsoriginal shape/size. As the spring biasing force moves the piston 94,the pivot pin 76 will move the balls disk 78 and the balls 82 containedtherein to engage the detents 84 and lock the short arm 70 relative tothe long arm 72 thereby prohibiting rotation.

An alternate embodiment is the use of opposing serrated surfaces actingagainst each other. For example if the detents on the short arm werereplaced by a series of radially spaced serrations about the pivot axisand the ball disk and balls were replaced with a disk containingradially spaced serrations, the serrations on the disk would engage theserration on the short arm, locking the short arm relative to the longarm and preventing rotation. The device would operate (lock and unlock)as described above.

A benefit of the above device is the ability to hold the pivot inposition without an external energy (power source) being applied. Thedevice remains fixed until the energy is placed into the actuator tofree the pivot and allow rotation. An additional benefit is the abilityof the device to slip or clutch when the device is placed under extremeloading, limiting damage to a closure, hinge or cargo. The lockingdevice 11 depicted in the FIGS. 16 through 19 can be used in used onsimple pivoting hinges or similar devices.

The locking devices 11 described above can be advantageously used for alarge number of cycles under varying ambient conditions. The lockingdevices employ active materials that permit an owner to adjust theattributes of the strut to suit the local climatic conditions and/orhis/her anthropometrics. They advantageously permit a dealer to adjustthese attributes at the point of sale to customize an otherwise massproduced vehicle for a specific buyer or they permit a service center toadjust the strut attributes to counteract the effects of wear. They canbe manually adjusted and controlled or computer adjusted and controlled.They can utilize feed back loops when desired. These adjustments couldbe made either via hardware tuning or via software changes.

While the disclosure has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims.

1. A strut assembly comprising: a piston in slideable communication witha housing; a locking device in operative communication with the piston,wherein the locking device comprises: an active material in operativecommunication with the device; wherein the device is operative tocontrol the motion of the piston and/or the motion of the housing. 2.The strut assembly of claim 1, wherein the locking device furthercomprises a sleeve, and the active material is in operativecommunication with the sleeve, such that the sleeve is operative tocontrol the motion of the piston and/or the motion of the housing. 3.The strut assembly of claim 2, wherein the active material is a shapememory alloy.
 4. The strut assembly of claim 2, wherein the sleeve is inoperative communication with a return spring.
 5. The strut assembly ofclaim 1, wherein the piston includes a piston head and a piston rod, thelocking device comprises a plate in operative communication with thepiston head, wherein the plate is in slideable communication with thepiston rod, a spring stack disposed between the plate and the pistonhead, and the active material is in operative communication with theplate, such that the active material upon activation is operative tocontrol the motion of the piston.
 6. The strut assembly of claim 1,wherein the piston includes a piston head and a piston rod, the pistonrod is in slideable communication with the housing, and the lockingdevice includes a protrusion fixedly attached to the piston head and awave-like tubular guide comprising the active material, such that thewave-like tubular guide is in slideable communication with theprotrusion and operative to control the motion of the piston.
 7. Thestrut assembly of claim 6, wherein the active material comprises a shapememory alloy polymer layer disposed on opposing surfaces of a shapememory alloy layer.
 8. The strut assembly of claim 1, wherein the pistonincludes a piston head and a piston rod in slideable communication withthe housing, and the piston head further includes a portion having oneor more elastic members, one or more brake shoes in operativecommunication with the elastic members, and an active material inoperative communication with the brake shoes and operative to controlthe motion of the piston.
 9. The strut assembly of claim 1, wherein thepiston includes a piston head and a piston rod in slideablecommunication with the housing, the housing includes anelectrorheological fluid or a magnetorheological fluid, the piston headincludes an optional permanent magnet and an electromagnet, and theoptional permanent magnet and the electromagnet are operative to controlthe motion of the piston.
 10. The strut assembly of claim 9, wherein theoptional permanent magnet and the electromagnet are concentricallyarranged.
 11. A locking device comprising: a pivot pin having disposedthereon a ball disk comprising balls; a long arm and a short arm inrotary communication with a pivot pin; wherein the short arm comprisesdetents disposed upon a surface that is opposed to a surface in contactwith a surface of the long arm; and a cylindrical housing incommunication with a surface of the long arm in opposition to a surfacein contact with the short arm, wherein the housing comprises anactuator, a piston and a spring, and wherein the actuator comprises ashape memory material operative to disengage the balls from the detents.12. A method of operating a strut assembly comprising: displacing asuspended body in mechanical communication with a piston; activating anactive material in operative communication with the piston; andcontrolling the motion of the suspended body.
 13. The method of claim12, wherein the activating of the active material occurs by theapplication of an external stimulus to shape memory material, andwherein the external stimulus is an electrical stimulus, a magneticstimulus, a thermal stimulus, a chemical stimulus, a mechanicalstimulus, an ultrasonic stimulus or a combination comprising at leastone of the foregoing external stimuli.
 14. The method of claim 12,wherein the activating of the active material resists the motion of thepiston.
 15. The method of claim 12, wherein controlling the motion ofthe suspended body comprises locking the suspended body.